Abstract:
The paper deals with batch soda cooking of pulp from rapeseed straw. The preliminary runs were focused on determination of active alkali charge and liquor-to-straw ratio upon the delignification degree of pulp. For suitable cooking parameters, viz. active alkali charge of 19 %, liquor-to-straw ratio of 5:1, and anthraquinone charge of 0.1 %, the effect of the delignification degree directly proportional to the H-factor upon the total yield, kappa number, and amount of rejects was investigated in the H-factor interval from 800 to 2,800 h. For soda-AQ cooks of straw, stalks, and silique valves, the total pulp yield, kappa number, as well as amount of rejects decreased with increasing H-factor. The greatest total yield and degree of delignification were found for soda-AQ pulp cooked from stalks only. On the contrary, the silique valves gave the lowest total yield. The degree of polymerisation of pulp cooked from straw, stalks, and silique valves increased with increasing H-factor, the greatest values were measured for pulp from stalks. The colour properties of pulp from straw and stalks including brightness found in the interval of 30 to 34 did not differ significantly each other. However, the tensile strength of handsheets made of pulp once dried and repulped was found to be markedly lower in comparison with never dried pulp.
